The present invention relates generally to the detection and treatment of Ehrlichia infection. In particular, the invention is related to polypeptides comprising an Ehrlichia antigen and the use of such polypeptides for the serodiagnosis and treatment of Human granulocytic ehrlichiosis (HGE).
Human granulocytic ehrlichiosis (HGE) is an illness caused by a rodent bacterium which is generally transmitted to humans by the same tick that is responsible for the transmission of Lyme disease and babesiosis, thereby leading to the possibility of co-infection with Lyme disease, babesiosis and HGE from a single tick bite. The bacterium that causes HGE is believed to be quite widespread in parts of the northeastern United States and has been detected in parts of Europe. While the number of reported cases of HGE infection is increasing rapidly, infection with Ehrlichia, including co-infection with Lyme disease, often remains undetected for extended periods of time. HGE is a potentially fatal disease, with the risk of death increasing if appropriate treatment is delayed beyond the first few days after symptoms occur. In contrast, deaths from Lyme disease and babesiosis are relatively rare.
The preferred treatments for HGE, Lyme disease and babesiosis are different, with penicillins, such as doxycycline and amoxicillin, being most effective in treating Lyme disease, anti-malarial drugs being preferred for the treatment of babesiosis and tetracycline being preferred for the treatment of ehrlichiosis. Accurate and early diagnosis of Ehrlichia infection is thus critical but methods currently employed for diagnosis are problematic.
All three tick-borne illnesses share the same flu-like symptoms of muscle aches, fever, headaches and fatigue, thus making clinical diagnosis difficult. Microscopic analysis of blood samples may provide false-negative results when patients are first seen in the clinic. The only tests currently available for the diagnosis of HGE infection are indirect fluorescent antibody staining methods for total immunoglobulins to Ehrlichia causative agents and polymerase chain reaction (PCR) amplification tests. Such methods are time-consuming, labor-intensive and expensive. There thus remains a need in the art for improved methods for the detection of Ehrlichia infection, particularly as related to HGE. The present invention fulfills this need and further provides other related advantages.
The present invention provides compositions and methods for the diagnosis and treatment of Ehrlichia infection and, in particular, for the diagnosis and treatment of HGE. In one aspect, polypeptides are provided comprising an immunogenic portion of an Ehrlichia antigen, particularly one associated with HGE, or a variant of such an antigen that differs only in conservative substitutions and/or modifications. In one embodiment, the antigen comprises an amino acid sequence encoded by a DNA sequence selected from the group consisting of (a) sequences recited in SEQ ID NO: 1-3, 5, 7, 16, 20, 34, 39-49; (b) the complements of said sequences; and (c) sequences that hybridize to a sequence of (a) or (b) under moderately stringent conditions.
In another aspect, the present invention provides an antigenic epitope of an Ehrlichia antigen comprising an amino acid sequence selected from the group consisting of sequences recited in SEQ ID NO: 30 and 51, together with polypeptides comprising at least two such antigenic epitopes, the epitopes being contiguous.
In a related aspect, DNA sequences encoding the above polypeptides, recombinant expression vectors comprising one or more of these DNA sequences and host cells transformed or transfected with such expression vectors are also provided.
In another aspect, the present invention provides fusion proteins comprising either a first and a second inventive polypeptide, a first and a second inventive antigenic epitope, or, alternatively, an inventive polypeptide and an inventive antigenic epitope.
In further aspects of the subject invention, methods and diagnostic kits are provided for detecting Ehrlichia infection in a patient. In one embodiment, the method comprises: (a) contacting a biological sample with at least one of the above polypeptides, antigenic epitopes or fusion proteins; and (b) detecting in the sample the presence of antibodies that bind to the polypeptide, antigenic epitope or fusion protein, thereby detecting Ehrlichia infection in the biological sample. Suitable biological samples include whole blood, sputum, serum, plasma, saliva, cerebrospinal fluid and urine. The diagnostic kits comprise one or more of the above polypeptides, antigenic epitopes or fusion proteins in combination with a detection reagent.
The present invention also provides methods for detecting Ehrlichia infection comprising: (a) obtaining a biological sample from a patient; (b) contacting the sample with at least two oligonucleotide primers in a polymerase chain reaction, at least one of the oligonucleotide primers being specific for a DNA sequence encoding the above polypeptides; and (c) detecting in the sample a DNA sequence that amplifies in the presence of the oligonucleotide primers. In one embodiment, the oligonucleotide primer comprises at least about 10 contiguous nucleotides of a DNA sequence encoding the above polypeptides.
In a further aspect, the present invention provides a method for detecting Ehrlichia infection in a patient comprising: (a) obtaining a biological sample from the patient; (b) contacting the sample with an oligonucleotide probe specific for a DNA sequence encoding the above polypeptides; and (c) detecting in the sample a DNA sequence that hybridizes to the oligonucleotide probe. In one embodiment, the oligonucleotide probe comprises at least about 15 contiguous nucleotides of a DNA sequence encoding the above polypeptides.
In yet another aspect, the present invention provides antibodies, both polyclonal and monoclonal, that bind to the polypeptides described above, as well as methods for their use in the detection of Ehrlichia infection.
In further aspects, the present invention provides methods for detecting either Ehrlichia infection, Lyme disease or B. microti infection in a patient. Such inventive methods comprise (a) obtaining a biological sample from the patient; (b) contacting the sample with (i) at least one of the inventive polypeptides, antigenic epitopes or fusion proteins, (ii) a known Lyme disease antigen and (iii) a known B. microti antigen; and (b) detecting in the sample the presence of antibodies that bind to the inventive polypeptide, antigenic epitope or fusion protein, the known Lyme disease antigen or the known B. microti antigen, thereby detecting either Ehrlichia infection, Lyme disease or B. microti infection in the patient.
Within other aspects, the present invention provides pharmaceutical compositions that comprise one or more of the above polypeptides or antigenic epitopes, or a DNA molecule encoding such polypeptides, and a physiologically acceptable carrier. The invention also provides vaccines comprising one or more of the inventive polypeptides or antigenic epitopes and a non-specific immune response enhancer, together with vaccines comprising one or more DNA sequences encoding such polypeptides and a non-specific immune response enhancer.
In yet another aspect, methods are provided for inducing protective immunity in a patient, comprising administering to a patient an effective amount of one or more of the above pharmaceutical compositions or vaccines.
These and other aspects of the present invention will become apparent upon reference to the following detailed description and attached drawings. All references disclosed herein are hereby incorporated by reference in their entirety as if each was incorporated individually.